The invention is generally directed to an improved aerator for liquids. More specifically, the invention is directed to an aerator for aspirating air into a livewell or baitwell.
It is known to use fishing boat livewell and baitwell aerators. For example, the inventor's own aerators disclosed in U.S. Pat. Nos. 4,865,776 and 4,927,568, hereby incorporated by reference into this application, have met with significant commercial success, and are in wide use in fresh water and salt water applications. One of the features of these aerators is a siphon break to prevent backflow of water from the livewell tank, which typically has a higher water level than the outside water source. This antisiphon feature requires that the aerator head be located above the tank water line. In some boats, valves or check valves are used to prevent backflow. In others, the aerator is used in a recirculating system with no connection to the outside water source. In the latter two cases, a simpler aerator can be used that does not need to be mounted above the water line.
A common aerator configuration for mounting below the water line is in the form of a 90.degree. elbow fitting, as shown in FIG. 1. As shown, the aerator fitting, designated generally as 14, typically has an inlet end 16 with a hose barb 17 for attachment to the outlet of the water supply pump (not shown), and threaded outlet ends 18A, 18B which pass through, and clamp to, the wall 19 of the livewell tank (not shown). An air tube 15 feeds air to the vacuum created by the water flowing through the fitting. It is desirable to locate the aerator low in the tank to replace stale water with fresh oxygenated water. The stale water is lifted out the overflow, or thoroughly mixed with the incoming oxygenated water.
One problem with the conventional aerator is that, for livewell and baitwell applications, it operates in an inefficient manner. (As used here, the term "livewell" is broader than its typical use, and encompasses any holding tanks, such livewells, baitwells or fishtanks, whether boat-mounted or not, which contain water or other liquids requiring aeration.) Thus, the conventional aerator requires excessive water velocity to create adequate aspiration, while also taking undue time to properly aerate (i.e., restore oxygen levels in) the tank. This slow aeration is due either to weak aspiration, or to small water port size which reduces water volume flow. To improve the oxygen restoration rate, water velocity must be increased still further with these aerators, requiring larger pumps and more power consumption, and resulting in more tank turbulence. Tank turbulence should be avoided because it can damage costly bait and/or game fish.
Also, significantly, the aspiration vacuum must be sufficient to overcome the water pressure created by cthe depth at which the aerator is situated. It has been found that the weak aspiration models cannot be mounted very far beneath the tank water level (i.e., less than 12 inches) or aeration will cease completely. Yet actual service often requires that the elbow be mounted 12 inches or more below the water surface.
It is also known to use hydrotherapy spa fittings to mix aspirated air with water. An example of such an aeration device is shown in FIG. 2. However, these fittings are designed to provide therapeutic massaging action using high velocity water and air flow.
The conventional livewell aerator shown in FIG. 1 develops a weak aspiration vacuum at the air inlet. This is due to the constant diameter liquid flow path and secondary flows which develop at the inside and outside bend regions of the elbow, and which act to reduce velocity in the aspiration region (see regions 75 of FIG. 8, showing the eddies which weaken aspiration). While the spa-type aerator shown in FIG. 2 develops a stronger aspiration vacuum, which is achieved by restricting the diameter of the liquid flow path, this also reduces the volume flow rate into the tank. In both the conventional aerators shown in FIGS. 1 and 2, the water velocity into the tank is high and potentially damaging to delicate bait and game fish.
Referring to FIGS. 7 and 8, the normalized output data for the conventional aerator also shows that the exit plane velocities can be as high as 2.5 times the average velocity at the elbow inlet, even though the flow path diameter is constant. This results in a strong stream of water shooting into the tank, potentially into the path of delicate bait or game fish.
The conventional aerator is also an inefficient design because the flow path is partially obstructed by the air inlet tube, which is positioned transverse to the water flow path. This creates a reduction in flow area at the air tube, and forces water flow to one side of the flow path. The flow develops and remains as a high velocity stream into the tank.
While the spa-type aerators (FIG. 2) use a more efficient area reduction to accelerate the water velocity and generate good aspiration vacuum, it has been determined that these aerators also have exit plane velocities 2.5 times the average inlet velocity, based on a ratio of their inlet to outlet areas.
The objective in a baitwell or livewell aerator is to generate a relatively high volume flow rate with a high air/water ratio, while also providing a modest outlet velocity. The outlet velocity should be sufficient to generate a circulating, oxygenating current in the tank without creating damaging turbulence. The aerator also must be designed to fit within the current size envelope if used on boats.
Accordingly, it is an object of the present invention to provide an improved aerator that can be used to generate a relatively high volume flow rate with a high air/water ratio, while also providing a relatively low outlet velocity which will not generate turbulence which can damage the livewell contents.
Another object of the present invention is to provide an aerator for livewell and baitwell applications which can generate a circulating current in the tank without creating damaging turbulence, and do so in an efficient manner.
Still another object of the present invention is to provide a livewell and baitwell aerator that can be used to aspirate air into the liquid flow at depths below one foot of water.